Gas heater for the production of gaseous plasma

ABSTRACT

Apparatus for the production of a gaseous plasma in a gas stream by means of an oscillatory electric current in which the gasconfining tube is positioned within a sheath and retained within the sheath by means of an annular retaining member secured to the sheath and having helical springs between the retaining member and the end of the tube to permit expansion and contraction of the tube as it is heated or cooled.

United States Patent Inventors Denis Cleaver [56] References Cited Thornton-in-Cleveland; UNITED STATES PATENTS Smkwmmms 2,694,774 1 171954 Clark 313/27 x A 1 No 768 1 8 2,963,603 12/1960 Germe'r 313/17 ff 0d16 968 3,249,781 5/1966 Smialek et a1.. 313/25 Patented J y 1971 3,340,415 9, 1967 De Ru1ter et a1. 313/231 X Assignee British man Products Company Limited FOREXGN PATENTS Billingham, Teesside, England 634,013 12/1963 France 313/146 Pnomy Primary Examiner-Roy Lake g s lgg Assistant Examiner-E. R. La Roche AttorneyBirch,Swind1er, McKie & Beckett GAS HEATER FOR THE PRODUCTION OF 5:35:32. 5 ABSTRACT: Apparatus for the production of a gaseous g plasma in a gas stream by means of an oscillatory electric cur- U.S.C1 313/22, rent in which the gas-confining tube is positioned within a 313/146, 313/231, 313/D1G. 6, 313/312 sheath and retained within the sheath by means of an annular lnt.Cl H0lj 7/26, retaining member secured to the sheath and having helical HOlj 61/28 springs between the retaining member and the end of the tube Field of Search 313/17, 25 to permit expansion and contraction of the tube as it is heated 49, 50, 51. 52, 42,146,148, 231, 312, 356, 22, 4 1 or cooled.

PATENTEU JULZT 1971 FIG! SHEET 1 [IF 3 I H t INVENTORS DENNIS CLEAVER ARTHUR LEONARD RILEY BY LMMM ATTORNEYS PATENTEU JUL27l97i 3 595 1 4 sum 2 OF 3 FIGZ INVENTORS DENNIS CLEAVER ARTHUR LEONARD RILEY BY 5,,5 M AdJ/Zr/du ATTORNEYS GAS HEATER FOR THE PRODUCTION OF GASEOUS PLASMA This invention relates to apparatus for the production of a gaseous plasma.

According to the present invention, apparatus for the production of a gaseous plasma comprises a gas-confining tube, a sheath enclosing said tube and defining a closed chamber surrounding said tube, sealing means to fluidtightly seal said tube within said sheath, retaining means to retain said tube within said sheath and resilient spring means between said tube and said retaining means topermit longitudinal expansion and contraction of said tube within said sheath whilst maintaining the tube fluidtightly sealed within said sheath.

Apparatus according to the present invention is used for the production of a gaseous plasma within the gas-confining tube by means of an oscillatory electric current of a suitable frequency. The apparatus additionally includes means for effecting an electric discharge within the tube and such means comprises an electrically conductive material mounted around the tube and connectable to a source of oscillatory electric current. Such means can be, for example, a copper tube having, say, from 3-10 turns around a portion of the gas-confining tube, for example from 4-9 turns.

ln operation, the gas-confining tube is heated by the plasma and thereby is caused to expand axially. It is desirable to cool the tube and to effect this the sheath surrounding the tube defines a chamber or jacket with the tube through which a cooling fluid can be passed. In such a construction, it is essential that the tube is fluidtightly sealed within the sheath to produce the cooling chamber or jacket and that suitablemeans are provided to permit the longitudinal expansion of the gas-confining tube to take place even when cooling of the tube is employed. Accordingly, the apparatus of the present invention includes resilient spring means positioned between the tube and a retaining member in order that axial expansion of the tube can take place whilst still maintaining the gas-confining tube in fluidtight engagement with the sheathfln addition, by appropriate design of the apparatus radial expansion of the tube can be accommodated without failure of the seal;

but in this case the radial expansion is accommodated by ensuring that-the apparatus is built to such tolerances that this is effected.

The resilient spring means can comprise a number of helical springs mounted to act around the circumference of the tube between thetube and a retaining member which is suitably an annulus mounted to be moveable towards and away from the end of the sheath by suitable securing bolts or nuts.

In addition, the apparatus usually includes a gas distribution head which can be provided with at least one inlet through which a supply of the gasin which the plasma is to be maintained can be introduced into the gas-confining tube. Normally a plurality of inlets will be arranged radially in the gas distribution head to produce within the gas-confining tube a spiral flow of the gaseous medium in which the plasma is to be maintained. In addition the gas distribution head can have a central bore through which additional gas or reactantstsolid or gaseous) can be introduced.

The gas distribution head, if desired, can be screwably located within a further annulus at one end on the end of the gas-confining tube which is provided with circumferential sealing means such as an O-ring of suitable material to engage with the internal wall of the sheath. This further annulus can be mounted to cooperate with the resilient spring means positioned between this annulus and the retaining member and thereby effect location and retention of the gas-confining tube within the sheath.

To permit adequate sealing of the apparatus against loss of fluid, it is desirable-that the various cooperating parts are provided with sealing means one between another.

The sheath can be provided with an annulus at its lower end forming an abutment against which the end of the gas-confining tube remote from the gas distribution head locates in fluidtight engagement 'via suitable sealing means such as an 'O-ring. The sheath can be provided with one or more inlet and outlet ports through which a liquid cooling medium can be supplied to, and withdrawn from, the cooling chamber between the sheath and the gas-confining tube and in addition connections to connect the electrically conductive material mounted around the tube with a suitable source of oscillatory electric current.

The sheath can be .formed from any suitable material usually an electrical insulator such as solid plastic material, for example nylon or polytetrafluoroethylene, providing that it has a softeningpoint in excess of the temperature-to which the cooling fluid will be heated during use of the apparatus.

The gas-confining tube will usually be formed of an electrically nonconductive material which is resistant to high temperatures such as silica or possibly of a conducting material with insulating strips of a nonconductive material and the gas distribution head can be formed from any suitable metal.

Two forms of the apparatus constructed in accordance with the invention will now be described by way'of example only with reference to the accompanying drawings in which:

FIG. 1 is a section through one form of the apparatus,

FIG. 2 is a section through part of another form of the apparatus, and

FIG. 3 is a section through a sheath to form a cooling jacket for the apparatus of FIG. 2. I

As shown in the drawing, the apparatus consists of a gasconfining tube 1 formed of silica located within a sheath 2 of nylon between which tubel and sheath 2 a cooling chamber 3 or jacket is thus for'medthrough which a cooling liquid can be passed to cool the gas-confining tube 1. The lower end of the tube 1 is provided with an annular abutment 4 which locates via an O-ring 5 on an annulus 6 which is attached to the sheath 2 by screws 7.

At its 'upper end the tube 1 is located by a locating member 8 having three locating studs 9, said locating member 8 being in the form of an annulus'with a circumferential channel 10 within which is positioned an O-ring 11 to form a seal between said locating member and a cylindrical insert 11a carried by nuts 24 to exert pressure on the annular member 11b at the top of sheath 2.

The gas distribution head 12 formed of two cooperating parts 13 and 14 is screwably mounted within the locating member 8, the gas distribution head 12 is provided with a central bore 15 and in addition a supply pipe 16 communicating with eight circumferentially spaced inlet ports l7 viachannel The upper end of the sheath 2 is provided with an annular retaining member 19 cooperating with a pressure member 20 having six circumferentially spaced springs 21 positioned between it and the locating member 8. The annular retaining member 19 is mounted on six spaced screw rods 22 attached by captive nuts 23 to the sheath 2 and the retaining member 19. can be axially moved along the rods 22 by means of wing pressure member 20 and thence on to the locating member 8.

A copper coil 25 having four turns is mounted around the lower portion of the gas-confining tube 1 andis connected through terminal members 26 to the exterior of the sheath 2. The sheath 2 is provided with an inlet port 27 and inlet member 28 connectable to a-source of cooling fluid. The sheath 2 additionally has an outlet port 29 in its wall connectable to an outlet member 30 positioned above the level of the inlet member 28.

In operation, a suitable gas in which the plasma is to be generated and maintained is supplied to inlet 16 to give vortex flow from 17. Additional gases may'be added through 15. A source of oscillatory electric current is supplied to the copper coil 25 surrounding said gas-confining tube 1 and a plasma initiated and maintained therein. A cooling fluid suitably water is introduced into the chamber 3 via the inlet member 28 and circulated through the chamber 3 and out through the connection 30 to cool the surface of the gas-confining tube 1. A typical oscillatory current has a voltage of from 3 kv. to 15 kv. and an amperage of from 40 to 300 and frequency from 1 mc./s to 10 mc./s.

The gas introduced into thetube to maintain the plasma within the tube can be, for example, a monatomic gas such as argon or helium or can be a diatomic gas such as nitrogen, oxygen or chlorine or a gaseous polyatomic compound such as titanium tetrachloride or silicon tetrachloride.

In addition to the gas distribution head supplying the gaseous medium in which the plasma is maintained, it can also be used to feed material into the gas-confining tube which is to be heated by the plasma. For example, gaseous additions such as volatile metal tetrahalides such as titanium tetrachloride or a silicon tetrahalide can be introduced into the tube via the central bore 15. Alternatively, solid particulate material can be fed into the tube via a probe through the central bore 15, a typical material being a finely divided titaniferous ore such as ilmenite.

As the plasma is maintained, the temperature of the gasconfining tube increases and the resulting expansion of the tube in an axial direction can take place by compression of the resilient springs 21 positioned between the pressure member 20 and a retaining member 8. Fluidtight sealing of the tube within the sheath is thus maintained throughout and on cooling the springs expand to permit the retraction of the tube to maintain the fluidtight sealing. v

The apparatus has the additional advantage that the gasconfining tube can be changed easily if necessary and different shaped gas distribution heads can be easily fitted without disturbing the position of the gas-confining tube within the sheath. Additionally the apparatus can be used with various sized gas-confining tubes.

As shown in FIGS. 2 and 3, an alternative form of apparatus is very similar to that shown in FIG. 1. In the apparatus shown in FIG. 2, the locating member 8 is sealed fluidtightly with a capping member 40 having a cylindrical portion 41 lying close the inner surface of the sheath as shown in FIG. 3. The screwed rods 22 are screwed into the sheath and maintained in the capping member and sheath by locknuts 42 and 43.

The individual single resilient springs as shown in FIG. I are replaced by a pair of helical springs 44 and 45 separated by an annular pressure member 46.

The sheath as shown in FIG. 3 consists ofa cylinder of nylon 47 provided with an outlet 48 and an inlet 49 for cooling fluid. Connections 50 and 51 are provided for connecting a coil of copper, not shown, to supply the oscillating current around the gas-confining tube, not shown. The sheath is recessed 52 and a cylindrical portion 53 of polytetrafluoroethylene is inserted in the recess to act as a heat shield'for the nylon tube 47. The recess 52 and heat shield 53 are positioned to lie adjacent the copper coil surrounding the gas-confining tube.

When 100 litres per minute of oxygen are fed through the apparatus shown in FIG. I or FIGS. 2 and 3 with oscillatory current being passed through the coil 25 from an oscillator having a plate power of 76.6 kilowatts then it is observed that the total power of the plasma produced is 32 kilowatts.

What we claim is:

I. A gas heater for producing gaseous plasma comprising a gas-confining tube having a gas inlet end and a gas discharge end,

a sheath coaxial with and surrounding said tube and extending longitudinally beyond said inlet end of said tube, said tube and said sheath being radially spaced apart to define a cooling fluid chamber therebetween,

first tube retaining means carried by said sheath and engaging said gas discharge end of said tube to retain said gas discharge end fixed against longitudinal movement relative to said sheath, said first retaining means being in sealing engagement with said sheath and said tube to seal one end of said cooling fluid chamber, I

a distributionhead capping and sealing said gas inlet end of said tube and having at least one gas inlet conduit for introducing gas to be heated into said tube, said distribution ead having attached thereto a radially outwardly extending flange having sealing means in slidable sealing contact with the inner surface of said sheath to seal the otherend of said cooling fluid chamber, whereby said distribution head can move longitudinally in said sheath while said other end of said cooling chamber remains sealed,

second tuberetaining means carried by said sheath for retaining said gas inlet end of said tube,

resilient means interposed between said second tube retaining means and said flange to permit longitudinal expansion and contraction of said tube within said sheath while maintaining said cooling chamber sealed, and

heating means positioned in said cooling fluid chamber and surrounding at least a portion of said tube.

2. A gas heater according to claim 1 wherein said resilient means comprises a plurality of helical springs having axes parallel to the longitudinal axis of said tube and being circumferentially spaced about said distribution head.

3.'A gas heater according to claim 1 wherein said second retaining means is axially adjustable with respect to said sheath.

4. A gas heater according to claim 1 wherein said first and second retaining means each comprise an annular retaining ring attached to said sheath, and wherein said flange is vremovably attached to said distribution cap whereby said distribution capcan be removed from said heater without unsealing said cooling fluid chamber.

5. A gas heater according to claim 1 wherein said resilient means comprises a plurality of pairs of helical springs arranged in series having axes parallel to the-longitudinal axis of said tube, one of said springs in each of said pairs acting against said retaining means and the other of said springs in each of said pairs acting against said flange, said springs in each pair being separated by an annular pressure member.

6. A gas heater according to claim 1 wherein said heating means comprises a heating coil connected to a source of oscillating electric current, and wherein said sheath includes connections to conduct oscillating electrical current to said heating coil.

7. A gas heater according to claim 1 wherein said gas inlet conduit is radially oriented to admit gas radially into said tube.

8. A gas heater according to claim 1 wherein said gas-confining tube and said sheath are of electrically insulative material. 

1. A gas heater for producing gaseous plasma comprising a gas-confining tube having a gas inlet end and a gas discharge end, a sheath coaxial with and surrounding said tube and extending longitudinally beyond said inlet end of said tube, said tube and said sheath being radially spaced apart to define a cooling fluid chamber therebetween, first tube retaining means carried by said sheath and engaging said gas discharge end of said tube to retain said gas discharge end fixed against longitudinal movement relative to said sheath, said first retaining means being in sealing engagement with said sheath and said tube to seal one end of said cooling fluid chamber, a distribution head capping and sealing said gas inlet end of said tube and having at least one gas inlet conduit for introducing gas to be heated into said tube, said distribution head having attached thereto a radially outwardly extending flange having sealing means in slidable sealing contact with the inner surface of said sheath to seal the other end of said cooling fluid chamber, whereby said distribution head can move longitudinally in said sheath while said other end of said cooling chamber remains sealed, second tube retaining means carried by said sheath for retaining said gas inlet end of said tube, resilient means interposed between said second tube retaining means and said flange to permit longitudinal expansion and contraction of said tube within said sheath while maintaining said cooling chamber sealed, and heating means positioned in said cooling fluid chamber and surrounding at least a portion of said tube.
 2. A gas heater according to claim 1 wherein said resilient means comprises a plurality of helical springs having axes parallel to the longitudinal axis of said tube and being circumferentially spaced about said distribution head.
 3. A gas heater according to claim 1 wherein said second retaining means is axially adjustable with respect to said sheath.
 4. A gas heater according to claim 1 wherein said first and second retaining means each comprise an annular retaining ring attached to said sheath, and wherein said flange is removably attached to said distribution cap whereby said distribution cap can be removed from said heater without unsealing said cooling fluid chamber.
 5. A gas heater according to claim 1 wherein said resilient means comprises a plurality of pairs of helical springs arranged in series having axes parallel to the longitudinal axis of said tube, one of said springs in each of said pairs acting against said retaining means and the other of said springs in each of said pairs acting against said flange, said springs in each pair being separated by an annular pressure member.
 6. A gas heater according to claim 1 wherein said heating means comprises a heating coil connected to a source of oscillating electric current, and wherein said sheath includes connections to conduct oscillating electrical current to said heating coil.
 7. A gas heater according to claim 1 wherein said gas inlet conduit is radially oriented to admit gas radially into said tube.
 8. A gas heater according to claim 1 wherein said gas-confining tube and said sheath are of electrically insulative material. 